1. Field of the Invention
The present invention relates to a magnetic resonant coupling wireless power transmission unit for transmitting power wirelessly using magnetic resonant coupling instead of electromagnetic induction or electromagnetic wave propagation. The present invention also relates to a power generator and power generation system for raising the voltage of electric energy, which has been generated by a power generating section such as a solar cell, by magnetic resonant coupling wireless power transmission.
2. Description of the Related Art
A solar power generation system ordinarily uses a so-called “solar cell module” in which a very large number of solar cells (which will be simply referred to herein as “cells”) are arranged inside a metallic frame and connected together. A glass plate is arranged in front of the solar cell module (which will be simply referred to herein as a “module”) so that the respective cells operate without being exposed to the air. And by assembling a number of such solar cell modules together, a solar power generation system can be established.
Use of such a solar power generation system, however, has not been widespread yet because the cost of manufacturing those cells and modules is too high, which is one of the major obstacles to its introduction. On top of that, the cost of establishing such a system by installing those cells and modules is also too high to neglect. Among other things, the higher the altitude of the place of installation, the riskier and the more expensive the installation work will be, which is a serious problem to overcome in order to further popularize the solar power generation system. What is more, to introduce a solar power generation system into an existing building, it is difficult to install the wiring connecting the solar power generating section outside of the building to electronic devices inside of the building, which is also one of the big problems with conventional solar power generation systems.
As will be described later, in a conventional solar power generation system, the output voltage of each of its cells is so low that a great many solar cells should be connected together to obtain a voltage that is high enough to operate an electronic device. And a decrease in reliability at such a very large number of connection points is a decisive factor in the decline of the long-term reliability of the overall system. In addition, if those modules and cables deteriorate with a long-term use, their replacements should also be installed at such a height. Consequently, the cost of maintenance is also non-negligible.
As a conventional solar power generator that would overcome such problems, a power supply system for supplying energy wirelessly from outside of a building and through the walls of the building has been proposed (see Japanese Patent Application Laid-Open Publication No. 2006-136045 (Embodiment 5 and FIG. 16), for example). Such a power supply system transmits RF (radio frequency) energy through the walls by electromagnetic induction.
On the other hand, United States Patent Application Publication No. 2008/0278264 (FIGS. 12 and 14) discloses a new type of wireless energy transfer system for transferring energy from one of two resonators to the other, and vice versa, through the space between them. The wireless energy transfer system couples the two resonators with each other via the evanescent tail of the oscillation energy of the resonant frequency that is produced in the space surrounding those two resonators, thereby transferring the oscillation energy wirelessly (i.e., by a non-contact method).
The power supply system disclosed in Japanese Patent Application Laid-Open Publication No. 2006-136045, however, cannot overcome the solar power generation device's own problem that the output voltage of each cell is low. In the field of solar power generation, a crystalline silicon based solar cell, which is currently used broadly due to its high energy conversion efficiency, has an output voltage Vc of just about 0.5 V. For example, if the DC output of a solar power generating section needs to be converted into AC power, the operation efficiency of a normal power conditioner is maximized in response to an input voltage of approximately 300 Vdc. That is why to get that conversion done with high efficiency, the output voltage of the solar power generating section should be increased to the vicinity of 300 V by connecting as many as several hundreds of cells together in series. On the other hand, if connected to a three-wire single-phase grid system (with a working voltage of 100 V or 200 V), which is a normal household wiring system, the solar power generating section may have its output voltage increased by a power conditioner as much as 200 fold or more. Considering the decrease in power efficiency to be caused by increasing the voltage that much, it is still preferred that a very large number of cells be connected together in series to increase the output voltage of the solar power generating section as much as possible.
It should be noted that even if the DC voltage is not converted into AC power within such a solar power generation system, a similar problem will also arise. For example, in a DC power supply system that has attracted a lot of attention these days, its working voltage will be either 48 Vdc or within the range of 300 to 400 Vdc. That is why even when solar energy needs to be supplied to a DC power supply system, several tens to several hundreds of solar cells also need to be connected together in series.
However, the greater the number of cells or modules to be connected together in series, the more easily the overall performance of the system will decline due to either so-called “partial shading” (i.e., some of the installation zone goes into the shade) or deterioration in the property of some of those cells or modules to be installed. To overcome such a problem, normally a countermeasure such as introduction of a bypass diode into each module is taken. Such a measure is not preferred because an excessive quantity of heat will be generated or the cost will rise significantly in that case. Meanwhile, even when the voltage needs to be increased using a normal DC/DC converter with a voltage boosting function, it is also difficult to achieve a voltage step-up ratio that is high enough to significantly reduce the number of cells to be connected together in series.
Also, the voltage boosting ability of the wireless energy transfer system disclosed in United States Patent Application Publication No. 2008/0278264 is limited to what should be realized by conventional transformer technology and is not sufficiently effective to overcome those problems to be solved by the present invention.